1. Field of the Invention
The present invention relates to a method for driving a plasma display and to a plasma display and more particularly to the method for driving the plasma display which is capable of avoiding an increase in costs for manufacturing the plasma display by omitting use of a costly forced-discharging circuit which is made possible by detecting, while power is off, a drop in a voltage fed from a main high-voltage power source and by changing a method of driving an X driver to cause an electric charge being left in an auxiliary high-voltage power source to be discharged, and to the plasma display.
The present application claims priority of Japanese Patent Application No. 2000-331184 filed on Oct. 30, 2000, which is hereby incorporated by reference.
2. Description of the Related Art
FIG. 4 is a diagram of a functional block explaining a conventional plasma display. In FIG. 4, there are provided an X driver 14, a signal control circuit 16, a voltage detecting circuit 17, a forced discharging circuit 18, contacts 21, 22, 23, and 24, lines for transmitting signals 31, 32, and 33, capacitors C1 and C2, a diode D1, ground potential terminals GND, a MOSFET M3 (Metal Oxide Semiconductor Field Effect Transistor), resistors R1, R2, and R3, an auxiliary high-voltage power source Vp and a main high-voltage power source Vs.
In the conventional plasma display as shown in FIG. 4, when any preventive measure against sequences in which power from a low-voltage power source Vcc (not shown), the main high-voltage power source Vs, and the auxiliary high-voltage power source Vp is turned OFF is not taken while the power is OFF, if the power from the low voltage power source Vcc (not shown) is turned OFF before the power from the main high-voltage power source Vs and auxiliary high-voltage power source Vp is turned OFF, a gate potential of a MOSFET (for example, a MOSFET M1 and a MOSFET M2 making up the X driver 14) being used in a high-voltage system reaches a level of floating, which causes a feed through current to flow in the MOSFET M1 and the MOSFET M2 due to noises or a like and also causes the MOSFET M1 and the MOSFET M2 to be damaged, in some cases. Conventionally, in order to protect circuits in a high-voltage system, a forced discharging circuit is provided to the main high-voltage power source Vs and the auxiliary high-voltage power source Vp and the power from the main high-voltage power source Vs and from the auxiliary high-voltage power source Vp is turned OFF before the power from the low-voltage power source Vcc (not shown) is turned OFF.
In the conventional method, as described above, to protect circuits in the high-voltage system, the forced discharging circuit 18 made up of the MOSFET M3 and the resistor R3 is provided. A drain of the MOSFET M3 is connected to the auxiliary high-voltage power source Vp, its gate is connected to the line for transmitting signals 33 and the resistor R3 is connected between the contact 24 and the ground potential terminal GND.
Moreover, a drain of the MOSFET M1 is connected through the contact 21 and the diode D1 to the auxiliary high-voltage power source Vp and the capacitor C1, its gate is connected to the signal control circuit 16 line for transmitting signals 31 and its source is connected to a drain of the MOSFET M2.
The drain of the MOSFET M2 is connected through the contact 22 to the source of MOSFET Ml and the capacitor C2 and its gate is connected to the line for transmitting signals 32, and its source is connected to the ground potential terminal GND.
The voltage detecting circuit 17 is mounted so as to detect a voltage at the contact 23 disposed between the resistor R1 connected to the main-high voltage power source Vs and the resistor R2 connected to the ground potential terminal GND.
FIG. 5 is a timing chart explaining operations of the conventional plasma display of FIG. 4. In FIG. 5, xe2x80x9cT1xe2x80x9d indicates a first time, xe2x80x9cT2xe2x80x9d indicates a second time, xe2x80x9cT5xe2x80x9d indicates a fifth time and xe2x80x9cT6xe2x80x9d indicates a sixth time.
Referring to FIG. 5, in the conventional plasma display, when the power is turned OFF at the first time T1, a voltage fed from the main high-voltage power source Vs (see FIG. 4) begins to drop and, when a voltage at the contact 23 reaches a predetermined voltage set by the voltage detecting circuit 17 at the second time T2, the voltage detecting circuit 17 operates to output to the line for transmitting signals 33. When the signal 33 goes high, the forced discharging circuit 18 operates and the voltage fed from the auxiliary high-voltage power source Vp becomes 0 (zero) at the fifth time T5. Then, after a lapse of the time set at a time when the power is turned OFF, at the sixth time T6 (T6 greater than T5), the voltage fed from the low-voltage power source Vcc (not shown) is lowered to 0 (zero) volts.
However, in the conventional method, since the forced discharging circuit 18 is introduced and the power from the main high-voltage power source Vs and the auxiliary high-voltage power source Vp is turned OFF before the power from the low-voltage power source Vcc (not shown) is turned OFF, though the damage in the MOSFET M1 and the MOSFET M2 can be avoided, introduction of an expensive forced discharging circuit causes manufacture of a PDP (Plasma Display Panel) to be costly.
In view of the above, it is an object of the present invention to provide a method for driving a plasma display which is capable of avoiding an increase in costs for manufacturing the plasma display by detecting a drop in a voltage fed from a main high-voltage while power is OFF and by changing a method for driving an X driver to cause an electric charge being residual in an auxiliary high-voltage power source to be discharged, thereby enabling an omission of use of a costly forced discharging circuit, and to provide the above plasma display.
According to a first aspect of the present invention, there is provided a method for driving a plasma display including a power source used to produce power from a low-voltage power source and a main high-voltage power source and a display section having a plasma display panel, an X driver and a Y driver each being used to drive the plasma display panel, a signal control circuit, a voltage detecting circuit used to detect a voltage fed from the main high-voltage power source and an auxiliary high-voltage power source, the method including:
a step of detecting a state of power-off by using the voltage detecting circuit used to detect a voltage fed from the main high-voltage power source while power is off and operating the X driver or the Y driver used to drive the plasma display panel to discharge electrical charges being left in the auxiliary high-voltage power source.
In the foregoing, a preferable mode is one that wherein includes a step of detecting a drop in a voltage fed from the main high-voltage power source while power is off and changing a method of driving the X driver to discharge the electrical charges being left in the auxiliary high-voltage power source.
Also, a preferable mode is one that wherein includes a step of detecting a drop in a voltage fed from the main high-voltage power source while power is off and changing a method of driving the Y driver to discharge the electrical charges being left in the auxiliary high-voltage power source.
Also, a preferable mode is one that wherein includes:
a step of stopping a supply of power fed from the main high-voltage power source and the auxiliary high-voltage power source when power is turned off at a first time and maintaining a voltage by using electrical charges being left in a capacitor for smoothing mounted in the main high-voltage power source and the auxiliary high-voltage power source;
a step of causing the voltage detecting circuit to operate to output a first signal when a voltage fed from the main high-voltage power source drops and a voltage at a first contact reach a level predetermined by the voltage detecting circuit;
a step of causing the signal control circuit having received the first signal to repeatedly produce a second signal and a third signal being out of phase with each other;
a step of causing a first MOSFET (Metal Oxide Semiconductor Field Effect Transistor) to be turned ON when the second signal goes high at a third time, which causes a voltage level at a second contact and a level of a voltage fed from the auxiliary high-voltage power source to reach {electrostatic capacity of the capacitor for smoothing mounted in the auxiliary high-voltage power source} multiplied by {potential of the auxiliary high-voltage power source} divided by ({electro static capacity of the capacitor for smoothing mounted in the auxiliary high-voltage power source} added to {electrostatic capacity of the capacitor for smoothing mounted in the main high-voltage power source}); and
a step of causing a second MOSFET to be turned ON when the third signal goes high at a fourth time, which causes the second contact to be discharged and a voltage at the second contact to reach a level of a ground potential, and when the operation is repeated, a voltage fed from the auxiliary high-voltage power source gradually drops and reaches 0 (zero) volts at a fifth time and, after a lapse of the time set at a time when power is turned off, a voltage fed from the low-voltage power source is lowered to 0 (zero) volts at a sixth time.
According to a second aspect of the present invention, there is provided a plasma display including:
a power source used to produce power from a low-voltage power source and a main high-voltage power source;
a display section having a plasma display panel, an X driver and a Y driver each being used to drive the plasma display panel, a signal control circuit, a voltage detecting circuit used to detect a voltage fed from the main high-voltage power source and an auxiliary high-voltage power source; and
wherein a state of power-off is detected by using the voltage detecting circuit used to detect a voltage fed from the main high-voltage power source while power is off and the X driver or the Y driver used to drive the plasma display panel operates to discharge electrical charges being left in the auxiliary high-voltage power source.
Also, a preferable mode is one wherein a drop in a voltage fed from the main high-voltage power source is detected while power is off and a method of driving the X driver is changed to discharge the electrical charges being left in the auxiliary high-voltage power source.
Also, a preferable mode is one wherein a drop in a voltage fed from the main high-voltage power source is detected while power is off and a method of driving the Y driver is changed to discharge the electrical charges being left in the auxiliary high-voltage power source.
Furthermore, a preferable mode is one wherein a supply of power fed from the main high-voltage power source and the auxiliary high-voltage power source is stopped when power is turned off at a first time and a voltage is maintained by using electrical charges being left in a capacitor for smoothing mounted in the main high-voltage power source and the auxiliary high-voltage power source and wherein the voltage detecting circuit operates to output a first signal after a voltage fed from the main high-voltage power source drops and a voltage at a first contact reach a level predetermined by the voltage detecting circuit and wherein the signal control circuit having received the first signal repeatedly produces a second signal and a third signal being out of phase with each other, and wherein a first MOSFET (Metal Oxide Semiconductor Field Effect Transistor) is turned ON when the second signal goes high at a third time, which causes a voltage level at a second contact and a level of a voltage fed from the auxiliary high-voltage power source to reach {electrostatic capacity of the capacitor for smoothing mounted in the auxiliary high-voltage power source} multiplied by {potential of the auxiliary high-voltage power source} divided by ({electrostatic capacity of the capacitor for smoothing mounted in the auxiliary high-voltage power source} added to {electrostatic capacity of the capacitor for smoothing mounted in the main high-voltage power source}), and wherein a second MOSFET is turned ON when the third signal goes high at a fourth time, which causes the second contact to be discharged and a voltage at the second contact to reach a level of a ground potential, and when the operation is repeated, a voltage fed from the auxiliary high-voltage power source gradually drops and reaches 0 (zero) volts at a fifth time and, after a lapse the time set at a time when power is turned off, the voltage fed from the low-voltage power source is lowered to 0 (zero) volts at a sixth time.
With the above configurations, while the power is OFF, by using the circuit used to drive the plasma display panel, the voltage fed from the auxiliary high-voltage power source can be lowered to the ground potential before the voltage fed from the low-voltage becomes the ground level and therefore the use of the costly forced discharging circuit becomes unnecessary which thus enables the cost-reduction to be achieved.